Field of Invention
The invention relates to a wobble plate type compressor especially for use in automotive air-conditioning systems, and more particularly, to a rotation-preventing mechanism for a wobble plate type compressor.
Description of the Prior Art
Wobble plate type compressors are well known in the art as disclosed, for example, in U.S. Pat. No. Re. 27,844. In the prior art, rotation of the drive shaft is converted into reciprocating motion of the pistons through a cam rotor having a sloping surface mounted on an end of the drive shaft and a wobble plate disposed on the sloping surface through a needle bearing therebetween. The wobble plate is supported on a fixed member in a manner that prevents it from rotating but allows it to nutate, or wobble. Thus, the wobble plate wobbles by the rotation of the cam rotor, and the piston rods connected to the wobble plate are reciprocated to compress fluid within the cylinders.
Referring to FIG. 1, which is a cross sectional view of a conventional wobble plate type compressor, the general structure of wobble plate type compressors will be explained. Compressor housing 1 is defined by crank chamber 11 and cylinder block 12 which is provided with a plurality of cylinders 121 axially disposed near the circumference of the cylinder block. One open end portion of housing 1 is covered by front end plate 2. Cylinder head 3 is mounted on the end surface of cylinder block 12 through valve plate 4 and affixed thereon by bolts 30.
Cylinder cavity 122 is formed at the center of cylinder block 12. Axial support device 5, which includes annular rod portion 51 with hollow portion 51a for disposing a coil spring (not shown) and bevel gear 52 formed on one terminal end of rod portion 51, is placed within cylindrical cavity 122. Key 123 is located in a groove defined on rod portion 51 of axial support device 5 and cylinder block 12 to prevent axial support device 5 from rotating. The center portion of bevel gear 52 is formed with seat portion 53.
Drive shaft 6 is rotatably supported in front end plate 2 through bearing 7 and is coupled at its inner end with cam rotor 8. Rotor 8 and the inner end of drive shaft 6 are disposed in crank chamber 11. Rotor 8 is axially and rotatably supported on the inner surface of front end plate 2 through bearing 9. Inclined surface 81 of rotor 8 is placed in close proximity to one end surface 101 of wobble plate 10 and is engaged with the wobble plate 10 by a bearing 13 located between cam rotor 8 and wobble plate 10. Bevel gear 14 is fitted on the central portion of wobble plate 10 by caulking and is provided with receiving seat 141 at its center. Bevel gear 14 interfits with bevel gear 52 through steel ball 15 to prevent the rotation of wobble plate 10. Accordingly, wobble plate 10 wobbles without rotation in response to the rotation of cam rotor 8.
A plurality of pistons 16 are reciprocally fitted within cylinders 121 and are connected to wobble plate 10 through connecting rods 17. As wobble plate 10 wobbles, pistons 16 reciprocate in cylinders 121.
Cylinder head 3 is defined by suction chamber 31 and discharge chamber 32. Discharge chamber 32 is located at the center of cylinder head 3 and suction chamber 31 surrounds discharge chamber 32. Inlet port 311 is formed on the outer end surface of cylinder head 3 for introducing refrigerant from a refrigerant circuit, and outlet port 321 is formed on the outer end surface of cylinder head 3 for discharging compressed refrigerant gas into the refrigerant circuit.
With reference to FIG. 2, a front view of wobble plate 10 with bevel gear 14 is shown. A plurality of receiving portions 102 for receiving one end of connecting rods 17 are spaced at regular intervals along the edge of wobble plate 10. Bevel geare 14 is fixed in the inner surface of wobble plate 10 by caulking portions 103. Wobble plate 10 is located with respect to bevel gear 14 so that point M, which is located at a center position between two teeth of bevel gear 14, is on a line drawn between the center point C of bevel gear 14 and a point P which is located at the center between two receiving portions 102. When wobble plate 10 and bevel gear 14 are combined with each other as described above, the center line of each connecting rod 17 is parallel to the center line of each cylinder 121, as shown in FIG. 3.
When the compressor is operated by rotating drive shaft 6, the axial force P.sub.1 of pistons 16 is in a direction parallel to cylinders 121 as shown by the arrow and dotted line in FIG. 4. The drag force on inclined surface 81 of cam rotor 8 is in the direction shown by the arrow and dotted line F.sub.1. Thus, a rotational force, as shown by dotted line and arrow F.sub.2, is created at the contact point between bevel gears 14 and 52 and tends to create an undesirable rotation in the wobble plate 10. This force F.sub.2 may be large enough to cause the rotation preventing mechanism provided in part by bevel gears 14 and 15 to break down and allow the wobble plate to rotate. At the very least, this force creates an undesirable level of vibration and noise at the bevel gears.